3. Phoned worked OK, except for Google Navigation (GN). Using GPS Test app, I could 'see' 5 - 8 satellites and eventually it did lock to 2 - 4 of those, but immediately thereafter when I launched GN, the phone did nothing and just sat there thinking and 'searching'...

4. To fix the above, I did a hard factory reset. This made things worse as now I don't even have an internet connection. Whether it is Google Play or a browser, it simply says "no connection"

My WIRELESS & NETWORKS settings look like this:

Data enabled - checked

Data roaming - unchecked

Network mode - GSM / WCDMA (auto mode)

Network operators --> Search networks --> do I ask it to select a network automatically or shall I select T-Mobile UMTS or T-Mobile GSM?

Any idea what else could be wrong / I am missing? Internet, Google Play and Gmail did work, they no longer do after I hard reset. I am sure I have an incorrect configuration, maybe the phone by default is trying to get to the net via the Spanish carrier it was originally locked to?

You can always flash it back to stock using NvIdia flash tool. I suggest flashing a UK version and if it bricks then flash it to another version. Its a win win here. If you need anymore help message me at jackdsparker.jp@googlemail.com